1. Field of the Invention
The present invention relates to a data compression device used for instance, when compressing data by means of the MPEG (Moving Picture Experts Group) technique for an authoring device. In this invention, when setting a target quantity of data for data compression based on the data quantity detected by the previous data compression process, the target data quantity are utilized in units of Group of Picture blocks and data is allotted to each frame in optimal amounts to achieve high image quality data compression of limited quantities of video data by correcting the structure of each Group of Pictures.
2. Description of Related Art
Currently, when a package media such as an optical disk has been fabricated, the various data for this optical disk such as audio data and video data compressed by techniques such as MPEG (Moving Picture Experts Group) are then multiplexed processed for recording onto various media.
In an authoring device implementing this kind of process, data compression of the video and audio data is performed in order to reduce the data bit quantity to an amount that can be recorded on the media and store the audio and video data within the allotted bit amount. Video data is allotted in a certain amount of bits to each frame according to the bit quantity yielded from the video data compressed under these set conditions.
In other words, when video data is compressed by the MPEG technique, the bit quantity after compression fluctuates greatly according to the material. The bit quantity after condensation also varies according to the coding within the frame and the coding process between frames.
In a data compression process for instance that maintains set data compression conditions, the authoring mechanism compresses the video data for recording onto an optical disk and detects sequentially, in frame units the bit quantity of compressed video data. Further, the data compression conditions are altered based on this detected bit quantity, causing the bit quantity assigned to the video data, to be allocated to individual frames according to the data quantity generated in the data compression process so that video data is suitably compressed.
Thus, the authoring device can efficiently record video data and audio data on a media with limited capacity, such as an optical disk.
However when setting data compression conditions based on bit quantities generated from the coding process used above, in actual operation, the target bit quantity for data compression is set for each frame and the coding conditions also set by the authoring mechanism. The process of setting the target data quantity is implemented by assigning allowable quantities of data to each frame according to the bit quantities generated by the coding process. Further, these frames which are set with the target data are corrected by the maximum transfer speed allowed by the optical disk. Finally, the video data is coded in sequence in compliance with the target bit quantity which has now been corrected according to these various conditions.
In the conventional authoring device using this kind of correction, the assigned target bit data sometimes could not ultimately be allocated correctly to the I picture, P picture, and B picture due to the difficulty involved in the process. So that assigning data in limited amounts and performing high quality video data compression was troublesome and difficult.